This invention relates to an ultrasound system and method for medical imaging, and in particular, for assisting in medical diagnosis using a catheter transducer.
Catheter transducers include catheter mounted transducer arrays. Catheter-mounted ultrasonic transducers have in the past taken several forms, including (1) single-element transducer crystals that are pointed radially outward and rotated about the axis of the catheter, (2) radial array transducers, and (3) linear array transducers. Bom U.S. Pat. No. 3,958,502 discloses one catheter-mounted ultrasonic array which utilizes a radial array arranged circumferentially around the axis of the catheter. Proudian U.S. Pat. No. 4,917,097 describes a similar radial array (and alludes to other geometries) that require multiplexing of the ultrasound signals near the elements of the array. Seward et al. (Seward, J. B., D. L. Packer, R. C. Chan, M. G. Curley, A. J. Tajik (1996), xe2x80x9cUltrasound Cardioscopy: Embarking on a New Journey,xe2x80x9d Mayo Clinic Proceedings, 71(7)) have described a phased array transducer for insertion into the heart. Such an array has the advantage of increased power: as the transducer array is made longer, the number of elements can be increased, thereby increasing the total radiation area.
Catheter transducer include intra-cardiac and intra-vascular transducers Intra-cardiac transducers are used to image tissue from inside a chamber of the heart. Intra-vascular transducers are used to image tissue from inside a vessel. Catheter transducers provide images of particular tissue with minimal interference from transmission and reception through multiple layers of other tissue.
Ultrasound imaging through multiple layers of tissue (e.g. by a transducer placed adjacent the skin of a patient) has been used to assess the health of tissue within the body. Methods that may be used for this assessment include Doppler based methods, such as Doppler imaging of tissue. In this method, Doppler based processing is used to measure the velocity of tissue within a region being examined. Knowledge of tissue movement, especially in relation to the motion of the neighboring regions, can indicate tissue health.
Perfusion measurements also provide diagnostic information. Perfusion is the blood flow per unit of tissue mass that supplies the tissue with oxygen and nutrients (volume/(time*mass)). Ultrasound systems may also be used to estimate perfusion. Methods for estimating perfusion include measuring the wash in and wash out times of contrast agents injected into the blood stream at a region of interest as the contrast agent enters and exits the region of interest.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiment described below includes a method and system for contrast agent imaging with a catheter transducer. As used herein, the catheter transducer includes intra-vascular, intra-cardiac or transducers for insertion into small spaces, such as the urinary tract. The catheter transducer is inserted within the heart or other portion of a patient. Contrast agents, such as micro-spheres, are injected into the patient. Using the catheter transducer, ultrasonic acoustic energy is transmitted, and reflected energy is received. The reflected energy is responsive to the contrast agents. An image processor generates an image of the tissue and contrast agents as a function of the reflected energy.
The image provides an indication of perfusion. Alternatively, the ultrasound system calculates perfusion. By generating intra-vascular images or data, interference from other tissues is avoided. Therefore, the perfusion information obtained may have higher resolution. Images with better resolution better assist doctors in medical diagnosis.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.